Micro-electrometer

ABSTRACT

A voltmeter for measuring atmospheric or other voltages eliminates the dead band without application of high voltages or radioactive isotopes to increase conductivity in the region of the probe. A vacuum tube is operated at substantially reduced conduction in order to achieve high sensitivity and eliminate passive components in the input circuit. A voltage is developed to produce meter indication or control charging or charge-neutralizing circuits. In the preferred embodiment, a meter scale is calibrated to indicate the presence of atmospheric charges of particular interest to anglers. Naturally occurring electrical currents are known to stimulate the feeding of fish.

CROSS REFERENCE TO RELATED APPLICATIONS

Not applicable.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

REFERENCE TO SEQUENCE LISTING, A TABLE OR A COMPUTER PROGRAM LISTINGCOMPACT DISK APPENDIX

Not applicable.

BACKGROUND—FIELD OF INVENTION

This invention relates to non-contact voltmeters, and to the indicationof atmospheric charges due to earth-air currents, as currents of anelectrical nature in bodies of water will also be impressed upon anyorganisms, i.e. fish, in the water, and electrical stimulus of theseorganisms will result.

BACKGROUND—DESCRIPTION OF PRIOR ART

The total of earth-air currents worldwide is accepted to be in the rangeof 1800 amps. These currents maintain the existence of earth'selectrostatic field, which varies from 100 to 1500 volts per meter nearthe earth's surface. Atmospheric charges and currents vary locally, andare influenced by cloud heights, moisture content, thunderstorms, jetstreams, wind, ionization due to solar radiation, conductivity of thelocation's soil or water, and natural or man-made topography orstructures. These currents will also be expressed in the earth'suppermost surface, and seek paths of least resistance. These may benatural or man-made paths not limited to metallic buried bodies such aspipelines, ore deposits, soils rich in ionic chemistry, and any body ofwater in conductive contact with the earth's surface.

Naturally occurring electrical currents are greatest in the vicinity ofthunderstorm activity, and certain levels of current peripheral to thesestorms are associated with air inflowing to updrafts, which results instrong winds and gusts depositing insects into the water, andassociation may be made between these conditions and the feeding offish.

A British patent of 1863 recognized electrofishing, in which fish areattracted to an anode conducting a direct current. Electrical stimulusof fish in their natural environment is recognized in U.S. Pat. No.5,445,111 (1995) to Smith, in which fish avoid a barrier presented by anelectrical current impressed in the water.

Non-contacting voltmeters are used in many applications tonon-intrusively measure electrostatic charges between bodies orsurfaces. The prior art has employed various methods to providesufficient sensitivity to measure small charges. The earlier devicesused vacuum tubes, as exemplified by Ecker et al, U.S. Pat. No.2,927,269 (1960). This voltage-measuring device requires ionization ofthe air at the probe by radium, which provides sufficient conductivityto complete a circuit through which enough current will flow to theground to permit meter indication. Ecker's device uses one of twopossible input resistances, in parallel with the control element, eitherof which were considered necessary in design, in which electronscollecting at the grid could leak off to ground. Without a return pathto ground for electrons, tube conduction stops as the grid becomes moreand more negative. This is true when tubes are operated at normalaccepted cathode temperatures and plate voltages. The current through atube is then so great, that a grid leak resistor is necessary to makethe tube and circuit stable, which decreases input sensitivity in thatit provides a leakage path to ground for the desired signal. The voltagedeveloped across the grid leak, applied to the control element, is notthe same voltage existing at the probe, but a representation of thevoltage derived as a result of current flow through the resistance.Ecker's device also uses a filament cathode, in which the electrons areemitted directly by a glowing wire, and undesirable current variationsin the filament circuit will deflect meter indication as readily as adesired signal. Other devices, such as L L Blackwell et al, U.S. Pat.No. 3,449,668 (1969), use a radioactive ionizing element, and twodirectly heated vacuum tubes arranged in a bridge circuit, but do notreduce cathode temperature to secure higher sensitivity or use a circuitproviding voltage amplification. Later non-contact voltmeters use aninput circuit based on a Field-Effect transistor (FET), often ametal-oxide silicon type (MOSFET), in which the gate of the devicecapacitively couples the signal of interest through a layer of silicondioxide 1000 angstroms thick. This thin layer is easily ruptured by aslittle as 100 volts, and typically is protected by one or more zenerdiodes in parallel with the gate, either integrally in manufacture, orincorporated into the circuit design. This degrades the input of theMOSFET in several ways: the leakage current is greater, and the inputresistance is less, because there is a diode across the input. Leakagecurrents of 10 sub-10 amps and input resistances of 10 sup 11 ohms aretypical for diode gate protected MOSFETs. Unprotected MOSFETs areunsuited to direct application of atmospheric potentials due to thelikelihood of gate rupture from electrical discharges. Anotherdisadvantage of the MOSFET is that it does not introduce the inputsignal directly into the stream of current to be modulated, but reliesupon opposing charges developed through a capacitor formed by thesilicon dioxide layer. These charges, a representation of the inputsignal, modify current-carrier mobility within a conduction channel.This capacitance introduces a 90-degree phase shift in any AC signal,and isolates a DC signal. Typically, an n-channel depletion type MOSFETis used in order to permit sensing voltage which may be negative orpositive. This type of FET has a nominally conductive channel of n-typematerial between its drain and source. Since the current in a FET is dueto the majority carriers (electrons for an n-type material), introducinga negative voltage to the gate induces positive charges into theconduction channel, which reduces the availability of majority carriers,decreasing conductivity. Such capacitive coupling is avoided in a vacuumtube; the actual input signal may be introduced upon a conductive pathto a point directly within the current to be modulated.

Voltmeters using solid state input devices suffer from an effectreferred to as “dead band.” This is a range between a small negativevoltage, through a zero-voltage point, to a small positive voltage,within which input current flow to a measuring device is insufficient todistinguish it from internal leakage currents due to input protection orleakage of the measuring device itself. In Govaert, U.S. Pat. No.4,950,978 (1990) conductivity of the air in the vicinity of the probe isincreased by application of high voltage AC coupled to the probe. Thiscreates ion pairs providing enough conductivity for a current to flow,sufficient to be measured by the sensing electronics. The applied highvoltage AC, corona discharge, and recombining ions and electrons createa large AC component, which must be filtered before the DC component canbe isolated. This design also uses a resistance in parallel with theinput, decreasing the sensitivity, and making the input voltage ananalog, rather than the actual input signal. Other electrostaticvoltmeters apply a high-frequency modulation to a capacitance betweenthe metering apparatus and the test surface to be measured.

The disadvantages in this method are that as the modulation frequency isincreased, smaller samples are collected for measurement. Low voltagesbecome increasingly hard to measure since they induce little currentinto a sampling capacitance. The resultant sample is a quantized charge,a function of the capacitance and the stability of the modulation andthe frequency used. Such a sample is derivative, not the actual inputsignal. This method is also somewhat intrusive as the modulatingfrequency imposed into a subject may result in rectification, resultingin a change of a DC level to be measured.

SUMMARY OF THE INVENTION

The invention consists of a non-contact voltmeter providing a very highinput impedance, permitting atmospheric or other voltage potentials todirectly control conduction of an electron tube, with operating voltagesspecifically limiting tube conduction to a low level, permitting thetube to achieve equilibrium with no grid current return path except thatprovided by the subject or environment to be measured.

OBJECTS AND ADVANTAGES

It is the object of the present invention to provide an accurate,durable, sensitive non-contact voltmeter for measurement of lowvoltages, particularly adjusted in this embodiment to advise anglers tothe presence of charges and currents known to stimulate fish. A furtherobject of the invention is to simplify the equipment needed to measurevoltages non-intrusively, by eliminating formerly required applicationof bias voltages, AC frequencies or ionization in the probe vicinity, orderivation of input voltages across passive components.

Another object is to provide a voltmeter useful in real-time measurementand control.

The first advantage of the invention is the use of reduced cathodeemission and tube conduction, which reduces the number of electronscollected by the control grid, making it possible to eliminate the gridleak resistor. This allows the actual test potential to influence thecurrent flow in the tube. It also allows the tube to create a self-bias,eliminating any need for user calibration.

The second advantage of the invention is the elimination of capacitancesbetween the sensor and the control element, providing true DC coupling,so that the actual potential to be measured is introduced upon thecontrol element, rather than an analog of it.

The third advantage of the invention is the use of an indirectly heatedcathode, with the result that minor current variations in the filamentdo not translate readily into deflection of the meter.

A fourth advantage of the invention is the durability of a vacuum tube,which is not subject to damage at low voltages, and not needing inputprotection, is not subject to reduced sensitivity caused by leakagecurrents in protection devices.

A fifth advantage of the invention is the conduction of the potential tobe measured directly to a point within the current flow to becontrolled, rather than influencing the flow of current from a pointadjacent, as a Field Effect Transistor does.

A sixth advantage of the invention is the elimination of any need toincrease conductivity in the vicinity of the probe by radioactive meansor high voltage corona discharge means, whether balanced or offset, andthe need for filter circuits to extract the desired signal from an ACvoltage created by such means.

A seventh advantage is the elimination of any need to derive ameasurement from quantized samples, or make tradeoffs between speed ofmeasurement and the size of the samples. This makes real-timemeasurement or control of a process possible.

An eighth advantage of the invention is the freedom of electron mobilitywithin the vacuum tube compared to the relative immobility of electronsin a semiconductor, within which electrons must migrate along specificpaths in a crystalline structure.

A ninth advantage of the invention is the adaptability of the circuit,in that adjustment of the various electrode voltages easily permit themeter to indicate a different range of voltage which may be of interestin a specific application, where the meter may be calibrated in current,any related microvolt relationship, or replaced by a load resistor todevelop a control voltage for process or environment control purposes.

A tenth advantage is the use of a vacuum tube with five grids, arrangedas a space-charge tube, with the control grid shielded electrostaticallyfrom the cathode and plate. This makes input capacity very smallpermitting a circuit arrangement providing voltage gain.

The increased operator safety, simplicity and other advantagesparticularly realized by this voltmeter arrangement will become apparentfrom a consideration of the drawings and ensuing description.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit diagram of an embodiment of the invention arrangedfor AC operation.

FIG. 2 is a circuit diagram of an embodiment of the invention arrangedfor battery operation.

LIST OF REFERENCE NUMERALS with PART DESIGNATIONS 17 switch SPST 23transformer 44 v. AC secondary 24 heater battery 2–1.5 v. D alkalinecells 25 rectifier 1N4004 silicon rectifier 26 plate battery 4–9 v.alkaline batteries 27 electrolytic capacitor 100 mfd. 50 v. 29 voltagedropping resistor 100 ohms 2 watt 33 screen resistor 2200 ohms, ¼ watt35 heater resistor 200 ohms 4 watt 37 tube 12BE6 (in socket) 37′ tube3BE6 or 6BE6 (in socket) 43 meter 1 ma./full scale 53 input terminal (onterminal strip) 54 ground terminal (on terminal strip) 55 neon bulb 57antenna 59 earth ground

DESCRIPTION OF THE INVENTION

FIG. 1 shows a schematic diagram of an embodiment of the inventionintended for continuous operation with a power supply arranged tooperate from standard alternating current. Referring to FIG. 1, anantenna 57, which may be a wire or a more elaborate structure at itsremote end, is placed as high as practicable, arranged and mounted in away as to provide electrical insulation from mounting structures thatmay be grounded. This antenna is connected by insulated wire to an inputterminal 53, one of two connections on a terminal strip. An earth ground59 is connected by insulated wire to a ground terminal 54, adjacent toinput terminal 53. Terminals 53 and 54 are the only external wiringconnections. All connections to a tube 37 are terminated through astandard plug-in tube socket (not shown). Tube 37 may be any tube typewhich may be operated as a space-charge tube. Input terminal 53 isconnected by wire to the third grid of tube 37, and to one side of aneon bulb 55. Terminal 54 is connected by wire to six points as internalground: the other side of neon bulb 55, the secondary of a transformer23, the negative terminal of an electrolytic capacitor 27, the negativeheater terminal of tube 37, the cathode and fifth grid terminal of tube37, and the first grid terminal of tube 37. A switch 17 is connected inseries with the primary winding of transformer 23, to the appropriate ACvoltage to be applied as power source. The other end of the primarywinding connects to the applied AC power source.

The secondary winding of transformer 23 is connected to the internalground wiring, and to the cathode of a rectifier 25. The anode ofrectifier 25 is connected to the positive terminal of electrolyticcapacitor 27. A voltage-dropping resistor 29 is connected at one end tothe positive terminal of electrolytic capacitor 27, at the other end, tothree points: a meter 43, a screen resistor 33, and a heater resistor35. The other terminal of meter 43 connects to the plate terminal oftube 37. Screen resistor 33 connects to the screen grid (second andfourth grids) terminal of tube 37. Heater resistor 35 connects to thepositive heater terminal of tube 37. FIG. 2 shows a schematic diagram ofan embodiment of the invention arranged for intermittent portableoperation from batteries.

Referring to FIG. 2, an antenna 57, which may be a wire or a moreelaborate structure at its remote end, is placed as high as practicable,arranged and mounted in a way as to provide electrical insulation fromstructures that may be grounded. In an outdoor situation this may be awhip-type antenna attached to the device itself rather than remote orelevated. The selected antenna is connected to an input terminal 53,directly in the case of the whip antenna, or by insulated wire in theother. Input terminal 53 is one of two connections on a terminal strip.An earth ground 59 is connected by insulated wire to a ground terminal54, adjacent to input terminal 53. These terminals 53 and 54 are theonly external connections. All connections to a tube 37′ are through aplug-in tube socket (not shown). Tube 37′ may be any tube type which maybe operated as a space-charge tube, with particular consideration givento reduced power consumption and matching commonly available batterytypes. Terminal 53 is connected by wire to the third grid terminal oftube 37′, and to one side of a neon bulb 55. Terminal 54 is connected bywire to 5 points as an internal ground: the other side of the neon bulb55, the negative heater terminal of tube 37′, the cathode and fifth gridterminal of tube 37′, the first grid terminal of tube 37′, and one sideof a switch 17. The other side of switch 17 connects to two points: thenegative terminal of a heater battery 24, and the negative terminal of aplate battery 26. The positive terminal of heater battery 24 isconnected to the positive heater terminal of tube 37′. The positiveterminal of a plate battery 26 is connected to two points: a meter 43,and a screen resistor 33. Meter 43 connects to the plate terminal oftube 37′. Screen resistor 33 connects to the screen grid (second andfourth grids) terminal of tube 37′.

OPERATION OF THE INVENTION

In usual practice, the voltages applied to a vacuum tube, whilepermitting use in high-impedance circuits, still permit too much gridcurrent to flow to allow atmospheric potentials to control theconduction of a tube. In this invention, both heater and plate voltagesare kept to such low levels as to permit only a very low level ofconduction, such that the flow of electrons in the tube is readilycontrolled by the charge introduced upon the third grid by the antenna.Control grid current is not eliminated by this operating condition, butreduced to a level that atmospheric currents provide the return path forthese electrons in the control grid circuit. The selection of tube type12BE6 is based upon its low inter-electrode capacities, hightransconductance and amplification factor.

Referring to FIG. 1, switch 17 is closed to provide AC voltage to theprimary winding of transformer 23. The secondary winding of thetransformer is connected to rectifier 25 and electrolytic capacitor 27forming a half wave rectifier power supply with a loaded output of 48volts DC.

Voltage dropping resistor 29 develops a 13 volt potential in operation.Voltage dropping resistor 29 is part of a voltage divider in series withheater resistor 35 setting the voltage to be applied to the heater oftube 37 to 9 volts. Voltage dropping resistor 29 is also in series withscreen resistor 33, setting the voltage to be applied to the second andfourth grids to 27 volts. Voltage dropping resistor 29 is also in serieswith meter 43, and the voltage applied to plate of tube 37 is 35 volts.These voltages applied to tube 37 result in a low emission of electronsfrom the cathode, and low current from cathode to plate. The voltage tobe measured at antenna 57 is applied to input terminal 53, which isconnected to the third grid of the tube.

The earth ground 59 is the reference signal to which a sample voltage iscompared, and is connected to terminal 54. Neon bulb 55 is not necessaryfor protection of the circuit or tube but as with any device attached toan elevated antenna, is provided as a lightning arrestor. This neon bulbwill ionize and conduct at a level of approximately 100 volts. Duringnormal operation, the neon gas is not ionized, and does not provide aleakage path for electrons in the grid to antenna circuit. The electronsemitted by the indirectly heated cathode are attracted to the positivelycharged plate of the tube. In traveling to the plate they must passthrough five concentrically arranged grids. The first and fifth of thesegrids are at ground potential, and electrons collecting upon them returnto ground. The second and fourth grids are connected by screen resistor33 and voltage dropping resistor 29 to positive potential, and electronscollecting upon them flow to the positive potential at the anode ofrectifier 25. As electrons flow from cathode to plate, and collect onthe five grids, a negative charge accumulates on the third grid, and aspace charge develops about this control grid, reducing the current fromcathode to plate. This accumulated charge is insufficient to cut offcurrent completely, which will achieve a low steady state. Meter 43connected between voltage dropping resistor 29 and the plate of tube 37will deflect a small amount, reflecting the small current flowing.Depending on the voltage applied between terminals 53 and 54, threedistinct conditions along a continuum may be indicated. In the case thatelectrons are neither collected by nor emitted from the antenna, anequilibrium state established by the tube operating point will result,with a small but definite meter deflection. This is also the case withno antenna connected. When the voltage present at the antenna isnegative, electrons collect upon the antenna, and being conducted to thethird grid of tube 37, the increasing negative charge on the gridreduces the current through the tube, decreasing plate current, anddeflecting the meter needle to a point lower than that indicated by theequilibrium state. In the case of a positive voltage at the antenna,electrons will be emitted by the antenna, supplied by the conductingwire from the third (control) grid of the tube, continuously replenishedby the space charge within the vacuum tube. These electrons return tothe cathode and negative side of the power supply through the atmosphereand earth. Under these conditions, plate current increases and the meterneedle deflects in a pronounced way to a position higher than thatindicated in the equilibrium state. This last condition ischaracteristic of the environment presented in the vicinity of weatherconditions creating currents in the earth's surface associated withwinds likely to deposit insects on the surface of lakes, rivers andstreams.

Referring to FIG. 2, switch 17 is closed to complete the circuitsenergized by heater battery 24 and plate battery 26. This applies 3volts to the heater of tube 37′, 36 volts to the plate of tube 37′through meter 43, and 27 volts to the second and fourth grids of tube37′ through screen resistor 33.

These batteries provide substantially the same potentials provided bythe half wave power supply and voltage divider network in the embodimentdescribed for alternating current operation, and establish the same lowconduction level for the tube.

All other aspects of operation are exactly as described for theembodiment operated by alternating current.

Description of Alternative Embodiments

The primary element of the invention is tube 37 or 37′, operating at avery low level of conduction. This condition is created by applying aheater voltage of approximately 71% of that normally specified for thetube type. The resulting low cathode temperature, combined withrelatively low plate voltage, permits elimination of a grid resistor,providing many useful possibilities. Further decrease of cathodetemperatures may provide an even greater sensitivity, but as conductionbecomes lower, additional stages of voltage amplification becomenecessary to develop a usable control voltage in the plate circuit. Atthe 71% level specified, a circuit with only one tube is sensitiveenough to develop a useful control voltage across a load resistor ormeter. Higher heater voltages increase cathode temperatures, and beginto create conditions in which a grid leak resistor would be necessary toprevent the control grid from developing a negative charge which wouldcut off tube conduction, thus decreasing sensitivity in a non-contactapplication. This could be desirable in a situation where a high-voltageenvironment is to be measured, as in the case of an electrostaticallycharged drum in a photocopy machine. Any power supply arranged toprovide the level of conduction as needed for a particular non-contactapplication could be used, with consideration of these issues.

An alternative embodiment might include a voltage comparator or simpleswitch to enable a visual or audible alarm indication at a user-selectedlevel.

Other embodiments might incorporate tube 37 or 37′, with other elementsreplaced by different power supplies and/or input signal arrangement.The voltages applied to plate, screen and heater may be lower or higherin order to permit indication of a different range of voltage. Thepolarity of signals applied between terminals 53 and 54 determines thedirection of meter deflection. Replacing screen resistor 33 with apotentiometer will permit the zero-voltage point to be calibrated tomid-scale on the meter, or any desired position, allowing for an offsetscale of either negative or positive. Particular applications willdictate whether terminal 53 should connect to positive or negativepotential relative to terminal 54.

Embodied in an electrostatic photocopy machine application, thepotentials for plate, screen, and heater voltages might be easilyprovided from other internal DC supplies. The input terminal and groundterminal would be replaced by connections to a probe near the field tobe measured, and an internal ground point. Meter 43 would be replaced bya load resistor, across which a voltage would be developed, to be usedto control the charging of the electrostatic drum.

Another embodiment might apply tube 37 or 37′ to derive a controlvoltage output to balance charges developed in semiconductormanufacturing equipment and facilities, to reduce the incidence offailed devices in manufacturing and assembly.

Systems that balance accumulated charges on aircraft might apply tube 37or 37′ to derive a control voltage for charge balancing.

Another embodiment might employ tube 37 or 37′ as a means for developinga control voltage to apply charges to powder handling equipment toimprove flows of materials, reduce dust and the likelihood of explosionsfrom electrical discharges.

Tube 37 or 37′ could be easily applied to measure a specific environmentin a burglar alarm. With adaptation the circuit would also be useful incontact applications, such a pH/ion meter. Another contact-typeapplication embodiment would employ tube 37 or 37′ in a circuit with theinput contacting two materials generating a work potential, as in athermocouple junction, or measuring work potentials in a laboratorysituation.

1. A non-contact voltmeter comprising: a source of power; a transformerengaged to the power source; an on/off switch engaged between the powersource and transformer; a terminal strip; an antenna engaged to an inputterminal of the terminal strip; an earth around engaged to a groundterminal of the terminal strip; a space charge tube comprising aplurality of grids and a plate; the input terminal of the terminal stripbeing engaged to one grid of the tube; a meter engaged to the plate ofthe space charge tube; a gas discharge tube engaged to an input of thetube; the tube at substantially reduced cathode temperature and electronemission, whereby voltages or other related quantities or qualities aremeasured in real time using only the naturally occurring voltage andconductivity present as a grid control source.
 2. The voltage of claim 1wherein the tube is operated at substantially reduced cathodetemperature and electron emission the sole direct current path forelectron communication between the control grid and the return side ofthe circuit being provided by the subject to be measured.
 3. Thevoltmeter of claim 1 wherein the tube is operated at substantiallyreduced cathode temperature and electron emission, utilizing only theconductivity of the subject to be measured to provide the grid controlsource, said circuit components being arranged to develop a voltage forindication by a meter.
 4. The voltmeter of claim 1 further including aheater resistor connected to a heater of the space charge tube.
 5. Thevoltmeter of claim 1 further including a screen resistor connected tothe grid of the space charge tube.
 6. The voltmeter of claim 1 furtherincluding a voltage dropping resistor connected to the screen resistorand the heater resistor of the space charge tube.
 7. The voltmeter ofclaim 1 wherein the source of power is an alternating current.
 8. Thevoltmeter of claim 1 wherein the source of power is a direct current. 9.The voltmeter of claim 1 wherein the gas discharge tube is a neon tube.